No abstract

In laboratory media, 10 of 16 isolates of Aspergillus versicolor from countrycured ham were capable of producing sterigmatocystin. Three of these isolates were tested and found to produce sterigmatocystin on country-cured ham after 14 days of incubation at 20 or 28 C.

A method is developed for computer simulation of the inactivation of microorganisms on items by irradiation. It is shown that in a population of items subjected to increasing doses of radiation the proportion contaminated approaches the appropriate Limiting Case, outlined in a previous paper, as numbers of organisms are decreased by inactivation. The behaviour of populations of items having different proportions of ‘spikes’ (high bioburden levels) is considered.

The numbers and types of microorganisms contaminating a commercially available laboratory animal diet were examined by plate-count methods at all stages of production. During the cooking and pelleting stages of manufacture there was a marked reduction in numbers of heat-labile vegetative contaminants introduced via the raw materials, and at subsequent stages plate counts at 37 and 25 degrees C corresponded closely to counts of viable aerobic bacterial endospores. It would seem that the count on the pelleted diet was determined principally by the numbers of bacterial spores being introduced with the ingredients. The response to gamma-irradiation of the innate microflora contaminating the pelleted diet was characteristic of that generally seen with populations of aerobic bacterial endospores.